Multi-source satellite observations as proxies for identifying changes in atmospheric pollutant indicators before and after the 2025 severe flood in Northern Sumatra, Indonesia.

Extreme flooding can alter atmospheric conditions through changes in emissions, surface conditions, and meteorological processes, yet assessing these changes remains challenging in regions with limited ground-based monitoring. This study examined satellite-derived atmospheric pollutant indicators before, during, and after the severe late-November 2025 flood in northern Sumatra, Indonesia, using multi-source satellite observations. Aerosol optical depth (AOD), AOD spatial coverage, and total-column NO₂, SO₂, and O₃ were analyzed using geospatial and statistical approaches. Significant temporal differences were observed across all indicators (Kruskal-Wallis test, p < 0.001). SO₂ showed the largest change, with lower levels during and after the flood than before the event. O₃ decreased during the flood and partially recovered afterward, while AOD magnitude declined during the flood and increased post-flood. In contrast, AOD spatial coverage expanded substantially after the flood, from 38.6 to 765.9 km² (p < 0.001), indicating broader detectable aerosol coverage despite changes in aerosol magnitude. Population-weighted analysis also showed differences in satellite-derived indicator changes across areas with different population sizes. Overall, the findings demonstrate heterogeneous temporal patterns in satellite-derived atmospheric indicators following severe flooding and highlight the utility of multi-source satellite observations for rapid regional assessment in data-scarce settings.